Greenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. Common greenhouse gases in the Earth's atmosphere include water vapor, carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons.

In our solar system, the atmospheres of Venus, Mars and Titan also contain gases that cause greenhouse effects.

Greenhouse gases, mainly water vapor, are essential to helping determine the temperature of the Earth; without them this planet would likely be so cold as to be uninhabitable.

In order, Earth's most abundant greenhouse gases are:

water vapor

carbon dioxide

methane

nitrous oxide

ozone

CFCs

When these gases are ranked by their contribution to the greenhouse effect, the most important are:

water vapor, which contributes 36-72%

carbon dioxide, which contributes 9-26%

methane, which contributes 4-9%

ozone, which contributes 3-7%

Where are greenhouse gases coming from and how have they changed?Many greenhouse gases, like water vapor and carbon dioxide (CO2), occur naturally. Fuel burning and other human activities are adding large amounts of carbon dioxide and other gases to the natural mix at a faster rate than at any other time on record.